The present embodiments relate to cement compositions and, in particular embodiments, to controlling the properties of cement compositions comprising a pozzolan and lime.
Cement compositions may be used in a variety of subterranean operations. For example, in subterranean well construction, a pipe string (e.g., casing, liners, expandable tubulars, etc.) may be run into a wellbore and cemented in place. The process of cementing the pipe string in place is commonly referred to as “primary cementing.” In a typical primary cementing method, to cement composition may be pumped into an annulus between the walls of the wellbore and the exterior surface of the pipe string disposed therein. The cement composition may set in the annular space, thereby forming an annular sheath of hardened, substantially impermeable cement (i.e., a cement sheath) that may support and position the pipe string in the wellbore and may bond the exterior surface of the pipe string to the subterranean formation. Among other things, the cement sheath surrounding the pipe string prevents the migration of fluids in the annulus and protects the pipe string from corrosion. Cement compositions may also be used in remedial cementing methods to seal cracks or holes in pipe strings or cement sheaths, to seal highly permeable formation zones or fractures, or to place a cement plug and the like.
A broad variety of cement compositions have been used in subterranean cementing operations. In some instances, set-delayed cement compositions have been used. Set-delayed cement compositions are characterized by being capable of remaining in a pumpable fluid state for at least about one day (e.g., about 7 days, about 2 weeks, about 2 years or more) at room temperature (e.g., about 80° F.) in quiescent storage. When desired for use, the set-delayed cement compositions should be capable of activation and consequently develop reasonable compressive strengths. For example, a cement set activator may be added to a set-delayed cement composition to induce the composition to set into a hardened mass. Among other things, set-delayed cement compositions may be suitable for use in wellbore applications such as applications where it is desirable to prepare the cement composition in advance. This may allow the cement composition to be stored prior to use. In addition, this may allow the cement composition to be prepared at a convenient location before transportation to the job site. Accordingly, capital expenditures may be reduced due to a reduction in the need for on-site bulk storage and mixing equipment. This may be particularly useful for offshore cementing operations where space onboard the vessels may be limited.
While cement compositions and set-delayed cement compositions have been developed heretofore, problems may exist when formulating these compositions for specific applications. For example, a composition with low reactivity may be desired such that the composition may maintain a low viscosity for applications requiring the cement composition to remain in a pumpable fluid state for as long period. However, such low reactivity fluids may not possess sufficient compressive strength when set to actually be suitable compositions for their intended use. Typically, cement compositions may use additives to enhance cement properties (e.g., compressive strength). However, additives may create additional costs as well as compatibility issues with other fluids or with the formation itself. Therefore, it may be desirable to adjust the properties of a cement composition while limiting the need to adjust the compositional makeup of the cement composition.